One of the cooling features included in modern graphics cards is a vapor chamber. Vapor chambers are occasionally mentioned in the marketing material for graphics cards – these marketing materials almost never cover what a vapor chamber actually is or does though.
What does a vapor chamber do?
A vapor chamber is a thin, relatively flat plate, that is used to spread heat over a wide surface area. Typically, a fin stack is applied directly to the surface of the vapor chamber to offer the maximum surface area possible for cooling via airflow.
Tip: A fin stack is a set of metal fins that are designed to maximize the surface area. Air being pushed by a fan then has a large surface area from which it can absorb heat more efficiently.
The vapor chamber is a hollow, vacuum-sealed copper plate. The point of the vapor chamber that is connected to the heat source, such as a GPU, is called the evaporator. When the evaporator is heated, the liquid in the wick evaporates into a gas. The hot gas then expands to fill the interior of the chamber, then once it reaches a cooler surface, the gas condenses again. The cooler surface is called the condenser. The condensed liquid is then returned to the evaporator through the wick, to continue the cycle.
Tip: A vapor chamber wick acts in exactly the same way that a candle wick does – it draws the liquid towards the heat source.
Why are vapor chambers so effective?
While metals such as copper are good at conducting heat, they are not the most efficient method. A large amount of thermal energy can be transferred to any material that goes through a phase change. A phase change is a transition from one form of matter to another, e.g. liquid to gas, or gas to liquid.
The process of evaporating the liquid in the vapor chamber into a gas transfers a large amount of heat energy to the gas. When the gas condenses again, this thermal energy is efficiently transferred to the condenser.
Alternatives to a vapor chamber
It would be possible to just use a solid copper block to perform a similar task, however, this design would be a lot heavier than a hollow vapor chamber. It would also be a lot slower at transferring heat away from the heat source to the cooling fins. This reduction in speed of heat transfer would affect the performance of the GPU as it would retain more heat.
Another alternative commonly used in CPU coolers are heat pipes. Heat pipes operate in a similar manner, with a phase change process. Heat pipes, however, can only really transfer heat from one end of the pipe to another, whereas a vapor chamber actively spreads that heat over a wide surface area. This difference in the surface area of the cooling end/side means that vapor chambers are more efficient at transferring heat to larger fin stacks, simply because it can be in direct contact with more fins than a heat pipe can be.